1. Field of the Invention
The present invention relates generally to concrete forms and has particular reference to new and improved articulated collapsible forms which are adapted for use in the formation of concrete structures such as a concrete culvert, a tunnel, or an elevator shaft. When the forms are used to provide a rectangular outline of an inside wall surface of a horizontally or vertically disposed corewall having chamfered corners, the corewall can be formed by pouring wet concrete around the form. With the unique double-hinge or two-way hinge construction that is provided in the types of forms herein disclosed, the forms can be collapsed inwardly away from the form walls so that the form is loosened from the hardened corewall-forming concrete and may then be shifted away from the formed wall into a position for use in connection with a subsequent concrete pour.
Concrete corewalls of the character under consideration are commonly employed in a horizontal position in connection with the creation of culverts, tunnels, or similar structures, or in a vertical position for elevator shafts, stairwells and the like.
2. The Prior Art
Heretofore, it has been the practice, when constructing an articulated collapsible concrete form for the inside surfaces of a rectangular corewall, to utilize a hinge joint at the midpoint of each of the two long sides of the rectangular form so that when the joints are broken inwardly, the articulated form collapses to produce a smaller form structure which has the outline of two truncated triangles which are connected in tandem fashion with their truncated corners joined together. The overall outline of such a collapsed form structure being smaller than the outline of the expanded form structure enables the collapsed structure to clear the walls of the hardened concrete of the corewall so that the collapsed form structure may be shifted longitudinally along the corewall to a new position for a subsequent concrete core or for removal purposes. Other types of collapsible concrete forms that have been used before are also shown in my U.S. Pat. No. 4,055,321, wherein three-way hinge assemblies are disclosed.
An articulated collapsible inside form structure of the character set forth above has certain limitations and an important object of this invention is to provide a new and improved two-way hinge assembly that can be used in a number of different types of forms for forming a variety of concrete wall structures having chamfered corners.